Why Brains Are Ugly

Let’s face it... brains are ugly and complicated looking

And we may be the worst offender! The problem is that much of the ‘architecture’ of the brain is not functionally meaningful F P O T

Santiago Ramon y Cajal ‘…to extend our understanding of neural function to the most complex human physiological and psychological activities, it is essential that we first generate a clear and accurate view of the structure of the relevant centers, and of the human brain itself, so that the basic plan – the overview – can be grasped in the blink of an eye.’ Histology of the Nervous System of Man and Vertebrates (1909)

Telencephalon (or ‘Cerebrum’) Swanson, 1995 Brainstem To Begin, Let’s Break the Brain into Two Functional Parts.

Telencephalon Cerebellum Diencephalon Hindbrain Spinal Cord Midbrain Superior Colliculus Inferior Colliculus Cortex Limbic System Basal Ganglia Thalamus Hypothalamus Now add in some sub-divisions Brainstem Brain Regions You Should KNOW

Human CNS Swanson, 1995 Tel: 81 Di: 4 Mid: 1 Hind: 2 Cblm: 10 SC: 2 Rat CNS Tel: 38 Di: 6 Mid: 4 Hind: 7 Cblm: 10 SC: 35 81

Zebra Finch CNS Tel: 64 Di: 6 Mid: 10 Hind: 6 Cblm: 10 SC: 4 Pigeon CNS Tel: 38 Di: 6 Mid: 12 Hind: 7 Cblm: 11 SC: 26 64

RatPigeonFinchHuman Telencephalon: Diencephalon:6664 Midbrain: Hindbrain:7762 Cerebellum: Spinal Cord:352642

S e n s o r y – D o r s a l M o t o r – V e n t r a l Hypothalamus Thalamus The Brainstem has a simple dorsal/ventral organization Dorsal Ventral When they are sick, Some Dogs Might Vomit Note the two sub-divisions of the diencephalon: Thalamus and Hypothalamus

Rat CNS Telencephalon Stimulus (what), motor control Thalamus relay, feedback (except olfaction) Spinal Cord reflexes, input, output Midbrain Stimulus (where) vision and audition only and orienting responses Primary Sensory Cortex Primary Motor Cortex Motor output Sensory input GENERAL Overview of Sensory System Organization (L/R and R/L crossing for vision, touch, audition only)

Rat CNS Telencephalon Primary Auditory Cortex Thalamus Medial Geniculate Midbrain Inferior Colliculus Hindbrain Pons, Medulla

Basal Ganglia Amygdala Hippocampus Cortex TELENCEPHALON AND DIENCEPHALON (some key subregions for S&P) Cortex Limbic Basal Ganglia Thalamus Hypothalamus Thalamus Hypothalamus Telencephalon Diencephalon

From Thalamus Back To Thalamus Output Layer CORTEX is made of Vertical Columns, each containing 6 layers of neurons

2D Receptor Array Thalamus Primary Cortex However…

Dense 2D Receptor Array Thalamus Cortex Is ‘Modular’ Means the size and density of cortical columns is fixed

Because Cortex is Modular, Sensory ‘Maps’ in Primary Cortex are Distorted by Variation in the Density of Sensory Receptors

A ‘homunculus’ of the USA Ha-ha! That looks funny!